Update mxcfb-kobo.h

Latest version (imx508/ntx, imx507), which, if I understand, covers the
latest Touch, the Glo and the Mini
Update mxcfb-kobo.h

To the latest available version (Kobo Aura).
The AuraHD appears to use the older version.
Minor comsetic tweaks to mxcfb-kindle.h
Tweak the kobo mxcfb cdecl
Update mxcfb ffi stuff